http://www.highrankings.com/

If you are low on budget and need affordable SEO:

http://www.affordable-search-engine-optimization-services.com/
References :
http://www.affordable-search-engine-optimization-services.com/

The plain fact is that there are very few excellent SEO companies but there are tens of thousands of SEO companies that advertise their poor quality services.

Good SEO companies are in great demand and the first thing NOT to do is use one that offers their services on Yahoo answers! No professional SEO that is any good has the time to solicit clients through such a medium or even needs to do so.

Here is the procedure I recommend.

Start by looking here http://www.seoconsultants.com/ which is about the nearest you can get to peer reviewed SEO consultants directory. Draw up a list of (say 10) companies whose web presence and spectrum of services meet with your approval.

Then make a simple initial approach to these companies and reduce the 10 to a short list of 3 or 4 based on the quality of their response (as you see it) and their understanding of your requirements.

Now interview the companies on your shortlist and include the following questions and requests:

1. Ask for 5+ references and current clients and make sure you follow them all up taking notes along the way.

2. What type of reporting will they provide?

3. Do they offer Return On Investment (ROI) analysis?

4. Can they assure you that the optimization strategies and methods used will be ethical and hence guarantee no penalties for your website?

5. Do they place a link on their clients sites to their site? If they do you can reject them right away.

6. Ask to see a sample contract. Check that it says ‘what is’ and ‘what isn’t’ required on the clients part and also details what they say they will do.

7. How many hours will they put into working on your site?

8. Make sure you will not be ‘ransomed’ if you decide not to use them any more at some stage.

9. Do they outsource any of the work? If they do you can reject them right away.

10. What results can you expect and over what time scales?

Once you have the answers to these questions for the companies on your short list you will find making a correct choice quite straightforward.

Good luck.
References :

What I would do is go to Google.com and type in your query and see what pops up. You should be able to find some info there. Hope this helps!
References :